Grinding mills are widely used in mineral processing applications and the most common types are the autogenous (AG) grinding mill in which the feed material itself acts as the grinding medium and the semi-autogenous (SAG) grinding mill in which supplementary grinding material, typically steel balls, is added to the feed material.
Grinding mills are often subjected to transient loads in the radial, axial and circumferential directions, particularly during start-up, if the material in the mill has settled and formed, what is commonly referred to as a ‘frozen charge’.
Gearless mill drives can be implemented in the form of an axial flux machine comprising a rotor disk and an axially adjacent stator. Particular difficulties can, however, arise due to the aforementioned transient loads which cause axial deflections of the rotor disk and therefore affect the air gap between the rotor disk and the axially adjacent stator. Unwanted vibration, fatigue and transient event damage can all result from the transient loads.
There is, therefore, a need for an improved axial machine which overcomes the aforementioned difficulties and which can be used as a gearless drive for a rotating electrical machine, and in particular a gearless mill drive for a grinding mill.